(a) Field of the Invention
The present invention relates to a fuel cell system. More particularly, the present invention relates to a reformer for receiving fuel and water and generating reformed gas and a water tank for supplying water to the reformer.
(b) Description of the Related Art
A fuel cell system basically includes a fuel cell stack, a fuel supply unit, and an oxidizer supply unit. The fuel cell stack receives fuel (hydrocarbon-based fuel, pure hydrogen, or hydrogen-rich reformed gas) and an oxidizer (air or pure air) from the fuel supply unit and the oxidizer supply unit, respectively, and generates electrical energy using an electrochemical reaction of the fuel and the oxidizer.
For example, in a polymer electrolyte fuel cell, a fuel cell system further includes a reformer for generating hydrogen-rich reformed gas by reforming hydrocarbon-based fuel. The polymer electrolyte fuel cell is complicated because it has to further include the reformer and its incidental units, but is suitable for a stationary installation type, such as for home use, because it has a high energy density and a high output.
The types of the reformer include a steam reformer, a partial oxidization reformer, and an autothermal reaction reformer. From among them, the steam reformer has a high hydrogen concentration of reformed gas and an excellent long-time operation stability. The steam reformer includes a reforming unit in which a chemical catalyst reaction resulting from heat energy of hydrocarbon-based fuel and steam is performed and a combustion unit (burner) in which the reforming unit is heated at a temperature of 750° C. or more in order to accelerate the chemical catalyst reaction of the reforming unit.
The reforming unit is connected to a fuel tank and is supplied with hydrocarbon-based fuel stored in the fuel tank when a fuel pump is operated. Further, the reforming unit is connected to a water tank and is supplied with water stored in the water tank when a water pump is operated. The combustion unit receives external air and the hydrocarbon-based fuel stored in the fuel pump and generates heat energy by combusting the fuel and the air.
In the above-described fuel cell system, when outside temperature goes down below zero, the water of the water tank is changed to ice. In this case, the fuel cell system cannot be used. To reuse the fuel cell system, you have to wait until the ice melts at above-zero temperature or to take a measure to melt the ice by, for example, installing hot wires in the water tank. However, a lot of time is taken to melt the ice at above-zero temperature. Further, in the case in which the hot wires are installed in the water tank, generating efficiency of the fuel cell system is lowered because additional power for driving the hot wires is required.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.